Hopf bifurcation control: A new approach

In this paper we find conditions to control a Hopf bifurcation in a class of nonlinear systems whose linear approximation has two eigenvalues on the imaginary axis, without assuming that the system is controllable. We use the center manifold theorem to project the dynamics on a two dimensional manifold, and design a controller that permits us to decide the stability and direction of the emerging periodic solution.     

Local feedback stabilization and bifurcation control, II. Stationary bifurcation

Local feedback stabilization and bifurcation control of nonlinear systems are studied for the case in which the critical linearized system possesses a simple zero eigenvalue. Sufficient conditions are obtained for local stabilizability of the equilibrium point at criticality and for local stabilizability of bifurcated equilibria. These conditions involve assumptions on the controllability of the critical mode for the linearized system. Explicit stabilizing feedback controls are constructed. The Projection Method of analysis of stationary bifurcations is employed. This work complements an earlier study by the same authors (Systems Control Lett.7 (1986) 11–17) of stabilization and bifurcation control in the (Hopf bifurcation) case of two pure imaginary eigenvalues of the linearized system at criticality.     

高速TCP/AQM中的RED算法分析

通过建立适用于高速TCP和AQM反馈控制系统的流体流模型,分析高速TCP/AQM闭环系统的稳定性。采用频域稳定裕度,得到高速TCP/AQM中RED算法的稳定参数区域。基于MATLAB/SIMULINK的仿真结果验证了该方法的有效性。     

松弛算法在TCP友好速率控制中的应用

由于TCP友好速率控制（TFRC）机制在实时多媒体应用中,TFRC流的发送速率波动性明显,不利于实时多媒体流的传输。采用松弛算法对TFRC流的发送速率进行自适应约束,使TFRC流发送速率在与TCP流竞争中变得更加平缓、收敛。实验结果表明,松弛算法能够改善TFRC的性能,提高实时流媒体的传输质量。     

TCP/AWM网络系统的事件触发预设性能拥塞控制EI北大核心CSCD

研究了具有非响应用户数据报协议流干扰的TCP/AWM网络系统的跟踪控制问题.针对网络拥塞控制系统,给出了一种改进的网络模型.将预设性能控制和事件触发机制相结合,提出了一种新的AWM拥塞控制算法.利用改进的边界性能函数限制TCP/AWM网络系统的队列跟踪误差,提高了闭环系统的暂态和稳态性能,保证了所有闭环信号都是有界的.此外,采用基于一位信号传输的事件触发控制协议,当控制信号更新时,仅通过一个二进制信号(0或1)传输信息.与传统的事件触发控制协议相比,不仅考虑了有限的带宽,而且考虑了网络传输的成本以及安全性问题.最后,通过仿真验证和分析,证明了所提方法的可行性和优越性.     

基于Fuzzy丢包区分的TCP自适应拥塞控制算法

针对在有线/无线的异构网络中,传统有线环境下的传输控制协议(TCP)把所有丢包简单地归因于网络拥塞,严重影响了混合网络环境下的TCP传输性能的问题,提出了一种新的基于模糊理论的自适应控制算法。该算法选取了新的网络参数,运用Fuzzy方法对网络状态进行综合评价,并基于反馈理论的方法建立了新的自适应控制模型,即对评价结果集进行加权求和,得出网络性能指数,将其作为输入因子进入下一次计算过程,并调整各参数权重。仿真表明,该算法能够较好反映混合网络的真实拥塞状况,具有较好的网络适应性,比当前主要TCP算法具有更好的拥塞控制效果。该算法对在多参数,使用模糊方法背景下,混合网络拥塞及其自适应控制研究进行了新的探索。     

无线网络TCP研究综述

如果把标准TCP直接应用于3种无线网络模型(蜂窝网络、Ad hoc网络和卫星网络),由于其不能够区分丢包的原因,可能会错误地启动拥塞控制,导致性能下降,分析了3种无线网络模型中影响TCP性能的因素,指出为减轻这些因素造成的负面影响所必须增加的一些额外技术,总结了提高无线网络TCP性能的一些方法并对这些方法进行了比较和分类,指明了无线网络TCP的研究方向。     

A neural network approach to characterize pattern parameters in process control charts

Abnormal patterns on manufacturing process control charts can reveal potential quality problems due to assignable causes at an early stage, helping to prevent defects and improve quality performance. In recent years, neural networks have been applied to the pattern recognition task for control charts. The emphasis has been on pattern detection and identification rather than more detailed pattern parameter information, such as shift magnitude, trend slope, etc., which is vital for effective assignable cause analysis. Moreover, the identification of concurrent patterns (where two or more patterns exist together) which are commonly encountered in practical manufacturing processes has not been reported. This paper proposes a neural network-based approach to recognize typical abnormal patterns and in addition to accurately identify key parameters of the specific patterns involved. Both single and concurrent patterns can be characterized using this approach. A sequential pattern analysis (SPA) design was adopted to tackle complexity and prevent interference between pattern categories. The performance of the model has been evaluated using a simulation approach, and numerical and graphical results are presented which demonstrate that the approach performs effectively in control chart pattern recognition and accurately identifies the key parameters of the recognized pattern(s) in both single and concurrent pattern circumstances.     

Fuzzy logic controlled RED: congestion control in TCP/IP differentiated services networks

The use of the Internet for time-sensitive services, such as voice and video applications, requires a predictable quality of service. The TCP/IP differentiated services (Diff-Serv) architecture was introduced to achieve such performance. Network congestion control, however, still remains a critical and high priority issue. A number of researchers are looking at alternative schemes such as random early detection (RED) and its variants to handle congestion. In this paper we present the results of a fuzzy logic control approach to the implementation of RED – Fuzzy-RED. We believe that with fuzzy logic we are able to use linguistic knowledge to implement better understood nonlinear probability discard functions, achieve better differentiation for packet discarding behaviors for aggregated flows, and so provide better quality of service to different kinds of traffic whilst maintaining high utilization.     

TCP-HY:优化TCP在混合IP网络环境中的效率

在混合网络环境下,由于数据包传输的非时序性以及在传输过程中相对较高的误码率,TCP的传输效率极大地被降低了。对此,提出了一种新的TCP改进版本:TCP-HY,它能够有效解决数据包延迟以及高误码率的问题。试验表明,TCP-HY在混合网络环境中能够大大提高TCP的效率,充分利用有效带宽,是一种优秀的解决方案。     

Dynamic queue level control of TCP/RED systems in AQM routers

One main TCP congestion control objective is, by dynamically adjusting the source window size according to the router queue level, to stabilize the buffer queue length at a given target, thereby achieving predictable queueing delay, reducing packet loss and maximizing link utilization. One difficulty therein is the TCP acknowledging actions will experience a time delay from the router to the source in a TCP system. In this paper, a time-delay control theory is applied to analyze the mechanism of packet-dropping at router and the window-updating in TCP source in TCP congestion control for a TCP/RED dynamic model. We then derive explicit conditions under which the TCP/RED system is asymptotically stable in terms of the instantaneous queue. We discuss the convergence of the buffer queue lengths in the routers. Our results suggest that, if the network parameters satisfy certain conditions, the TCP/RED system is stable and its queue length can converge to any target. We illustrate the theoretical results using ns2 simulations and demonstrate that the network can achieve good performance and converge to the arbitrary target queues.     

TCP Yuelu:一种基于有线/无线混合网络端到端的拥塞控制机制

无线链路传输数据的比特率出错导致TCP协议在有线／无线混合网络环境下性能低下,在改进算法TCPReno的基础上,文章提出了一种适用于有线／无线混合网络的拥塞控制机制,该机制包括一种分阶段平滑慢启动机制,改善了突发流量对网络性能的损害,引入网络测量技术获得了往返时间（RTT）、网络带宽、瓶颈链路队列长度等网络状态参数,区分网络拥塞和无线链路比特差错,避免了终端节点对网络状态不了解产生的盲目行为,有效改进了TCP的加性增加乘性减少（AIMD）窗口调节机制,提高了网络性能．同时,在仿真软件NS2中实现了该算法,进行了大量的仿真实验,实验结果表明TCP Yuelu有效降低了网络抖动,提高了网络传输性能,并保持了良好的公平性和对其它TCP流的友好性．     

Multiclass AQM on a TCP/IP router: A control theory approach

Active queue management (AQM) is a well‐known technique to improve routing performance under congested traffic conditions. It is often deployed to regulate queue sizes, thus aiming for constant transmission delay. This work addresses AQM using an approach based on control theory ideas. Compared with previous results in the literature, the novelty is the consideration of heterogeneous traffic, ie, multiclass traffic. Thus, each traffic class may have different discarding policies, queue sizes, and bandwidth share. This feature brings the proposal nearer to real network management demands than previous approaches in the literature. The proposed technique assumes that each class already has a simple controller, designed a priori, and focuses on designing a static state‐feedback controller for the multiclass system, where the design is based on using LMIs for the calculations. For this, optimization problems with LMI constraints are proposed to compute the state‐feedback gains that ensure stability for a large set of admissible initial conditions. These conditions ensure not only closed‐loop stability but also some level of performance. As far as we know, this is the first control theory based approach for the AQM problem on TCP/IP routers that allows a multiclass AQM while also considering time‐varying delays and input saturation. This is an important step to frame AQM in a more formal, yet realistic context, enabling it to address important service level agreement (SLA) directives. The proposal is tested on a simulated system at the end of this paper, showing the feasibility and performance of the approach in the presence of multiclass traffic.     

TCP/IP networking in process control plants

This paper refers to the utilization of Transmission Control Protocol/Internet Protocol (TCP/IP) in process control plants. Pertinent characteristics of classical control systems are presented, as a base to comparison with TCP/IP control systems. The advantages and shortcomings of adopting the latter one are pointed out. Integration with Internet-based technologies and systems management is explained next. Some products that provide these features are also presented as well as common components used in corporate networks, which can fully exploit and enhance the versatility of these control networks. Finally, economical aspects of this design are briefly commented.     

A new method to determine the periodic orbit of a nonlinear dynamic system and its period

Periodic motion is an important steady-state motion in the real world. In this paper, a new generalized shooting method for determining the periodic orbit of a nonlinear dynamic system and its period is presented by rebuilding the traditional shooting method. First, by changing the time scale, the period of the periodic orbit of a nonlinear system is drawn into the governing equation of this system explicitly. Then, the period is used as a parameter in the iteration procedure of the shooting method. The periodic orbit of the system and the period can be determined rapidly and precisely. The requirement of this method for the initial iteration conditions is not rigorous. This method can be used to analyze the forced nonlinear system and the parameter exciting system. As an example, the results of the Rössler equation for an eight-dimensional, nonlinear, flexible, rotor-bearing system are compared with those obtained by the Runge-Kutta integration algorithm. The validity of this method is verified by the numerical results obtained in the two examples.     

A new approach to adaptive control: no nonlinearities

In adaptive control the goal is to design a controller to control an uncertain system whose parameters may be changing with time. Typically the controller consists of an identifier (or tuner) which is used to adjust the parameters of a linear time-invariant (LTI) compensator, and under suitable assumptions on the plant model uncertainty it is proven that good asymptotic behaviour is achieved, such as model matching (for minimum phase systems) or stability. However, a typical adaptive controller does not track time-varying parameters very well, and it is often highly nonlinear, which can result in undesirable behaviour, such as large transients or a large control signal. Furthermore, most adaptive controllers provide only asymptotic tracking, with no ability to design for a pre-specified settling time.Here we propose an alternative approach, which yields a linear periodic controller. Rather than estimating the plant or compensator parameters, instead we estimate what the control signal would be if the plant parameters were known. In this paper we argue the utility of this approach and then examine the first order case in detail, including a simulation. We also explore the benefits and limitations of the approach.     

A layered approach to network management control

Public telecommunications networks have many supporting operations systems to provide network management functions and operational support. These systems must be coordinated to provide a highly reliable network service and to make best use of network resources. With increasing automation of network control, these systems must evolve to provide total network support. One organizing principle for this evolution is the definition of control layers at which individual control functions are exercised. We describe a proposal for layered control, with particular emphasis on the role of network traffic management. Layering will be a significant study item for the next extensions to CCITT's Telecommunications Management Network (TMN) recommendations.     

A new approach to averaging level control

In this paper, a new simple algorithm for averaging level control is presented. The proposed algorithm is based on the use of a static nonlinear controller to improve the input flow filtering by reducing the slope of the controller around the average input flow. In order to adapt the controller to changes in the average input flow, a low-pass filtered value of the estimated input flow is used to update the nonlinear function that defines the static controller. The stability of the closed loop is demonstrated, and the validity of the proposed strategy is tested in simulations and on a real oil refinery process.     

High level planning and control: An IDEF0 analysis for airframe manufacture

This paper presents an overview of a high level planning and control system (HLPCS) designed to permit CAD/CAM integration of the manufacturing processes of a generic airframe manufacturing facility. This analysis was performed in part under the direction of the United State Air Force Integrated Computer Aided Manufacturing Program (project priority 6104). The analysis was conducted through the design/communication tool of IDEF₀ (ICAM definition language). This paper will therefore rely heavily on discussions utilizing IDEF₀. The concepts of the HLPCS will be discussed, the aspects of the system enhancements that encourage integration will be highlighted, and conclusions regarding system improvements will be identified.     

Designing economic np control charts: A programmed simulation approach

This paper presents control charts models and the necessary simulation software for the location of economic values of the control parameters. The simulation program is written in FORTRAN, requires only 10K of main storage, and can run on most mini and micro computers. Two models are presented - one describes the process when it is operating at full capacity and the other when the process is operating under capacity. The models allow the product quality to deteriorate to a further level before an existing out-of-control state is detected, and they can also be used in situations where no prior knowledge exists of the out-of-control causes and the resulting proportion defectives.